1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for minimizing slack in continuous drive members, such as chains, belts, cables, and the like, in variable temperature environments. Embodiments of the invention may be utilized in apparatus for the forming of layers on a substrate used to form electronic devices, such as a solar cell device.
2. Description of the Related Art
In the manufacture of electronic devices, such as photovoltaic (PV) or solar cells, circuits are formed on substrates in process chambers that are cycled between room temperature (e.g., about 20 degrees Celsius (C) to about 25 degrees C.) and processing temperatures, such as about 300 degrees C., or greater. In some of the circuit formation processes, substrates are transferred into and through the process chambers on conveyors utilizing one or more continuous drive members that facilitate movement of the conveyor and substrates thereon. The continuous drive members may be a belt, a chain, a cable, as examples, which are made of metallic materials chosen for mechanical strength, as well as other criteria, when used in these variable temperature environments.
However, the continuous drive members are subject to elongation in the variable temperature environments due to coefficients of thermal expansion associated with the specific material of the drive member. The elongation in the drive member produces slack, which may cause the drive member to slip or otherwise lose the ability to provide a controllable drive function. The elongation may also shorten service life in the drive member as well as other parts that facilitate movement of the drive member, such as sprockets, pulleys or sheaves.
Conventional tensioners may be used to mitigate the slack. However, conventional tensioners that may be used in variable temperature environments exert a substantial tensional force on the drive member at room temperature, which applies an unnecessary load on the drive member. The excessive load may shorten service life in the drive member as well as other parts that facilitate movement of the drive member. Additionally, an increase in the temperature of these conventional tensioners tends to reduce the spring constant in these conventional tensioners, which impedes or may even prevent proper tensioning of the drive member at higher temperatures.
Therefore, there is a need for an improved tensioner that facilitates controllable operation of the drive member as well as extending the service life of the drive member.